2027 ICD-10-CM Diagnosis Code R99Ill-defined and unknown cause of mortality
ICD-10-CM Codes›R00–R99›R99›R99
- Billable — Valid for Submission
- Not Chronic
R99 is a billable ICD-10-CM diagnosis code for ill-defined and unknown cause of mortality. It is valid on HIPAA claims for fiscal year 2027 (October 1, 2026 through September 30, 2027) and groups to MS-DRG 951. As a symptom code, it should not be used as a principal diagnosis once a related definitive diagnosis has been established. In AHRQ's Clinical Classifications Software (CCSR), this diagnosis falls under Other general signs and symptoms.
Code Identity
Code Classification
Approximate SynonymsGuidance
Alternate terms and clinical phrases that map to this code.
- Accidental death
- Accidental death in home
- Accidental death in industrial place
- Accidental death in public place
- Accidentally killed
- Adverse incident outcome
- Anesthetic death
- Antepartum maternal death
- Autopsy pending
- Autopsy performed
- Child death
- Clavien-Dindo classification finding
- Clavien-Dindo classification grade V
- Dead
- Dead - death without witness
- Dead - expected
- Dead - sudden death
- Dead - suspicious death
- Dead - unexpected
- Dead on arrival at hospital
- Death
- Death as outcome of adverse incident
- Death associated with influenza
- Death associated with respiratory syncytial virus infection
- Death by asphyxiation
- Death by fire
- Death by hanging
- Death by immolation
- Death due to chemotherapy toxicity
- Death due to radiotherapy toxicity
- Death due to trampling
- Death during anesthetic induction
- Death from direct obstetric cause occurring more than 42 days but less than one year after delivery
- Death from indirect obstetric cause occurring more than 42 days but less than one year after delivery
- Death from overwork
- Death from sequela of direct obstetric cause
- Death from sequela of indirect maternal cause
- Death in home
- Death in hospice
- Death in hospital
- Death in hospital-based emergency department
- Death in hospital-based emergency department or outpatient department
- Death in hospital-based outpatient department
- Death in less than 24 hours from onset of symptoms
- Death in long term care facility
- Death in nursing home
- Death in nursing home or long term care facility
- Death of unknown cause
- Death unattended by physician
- Died at home
- Died during operation
- Died in ambulance
- Died in care home
- Died in community hospital
- Died in general practice premises
- Died in hospice
- Died in hospital
- Died in learning disability unit
- Died in mental health unit
- Died in nursing home
- Died in street
- Died in usual place of residence
- Died without sign of disease
- Direct maternal death
- Early neonatal death
- ECOG performance status - grade 5
- ECOG performance status finding
- Fetal disorder due to maternal death
- Found dead
- Found dead at accident site
- Found dead in bed
- GRACILE syndrome
- Iatrogenic death
- Indirect maternal death
- Infant death
- Instantaneous death
- Intraoperative death
- Intraoperative or immediately postoperative death in an ASA Class I patient
- Intrapartum maternal death
- Killed
- Late maternal death
- Late neonatal death
- Maternal death
- Maternal death - perinatal
- Natural death
- Natural death reportable to medicolegal authority
- Natural death with probable cause suspected
- Natural death with proved cause
- Natural death with proved cause by autopsy
- Natural death with proved cause without autopsy
- Natural death with unknown cause
- Neonatal death
- Non-traffic vehicular accidental death
- Patient death associated with a fall while being cared for in a healthcare facility
- Patient deceased during stay
- Patient status determination, deceased
- Patient status determination, deceased and body cremated
- Patient status determination, deceased and body donated
- Patient status determination, deceased and buried
- Patient status determination, deceased and entombed
- Patient status determination, deceased and removed from state
- Perinatal death
- Perioperative death
- Postmortem plain X-ray abnormal
- Postmortem rigidity
- Postneonatal death
- Postoperative death
- Postpartum maternal death
- Preoperative anesthetic death
- Serious reportable event associated with environment
- Sudden death
- Sudden death of unknown cause during the puerperium
- Sudden death, cause unknown
- Sudden infant death
- Sudden infant death syndrome
- Sudden infant death with dysgenesis of testes syndrome
- Sudden unexpected death in epilepsy
- Suspicious death
- Traffic vehicular accidental death
- Unattended death
- Unattended death of unknown cause
- Undetermined manner of death
- Undetermined manner of death, natural causes suspected
- Undetermined manner of death, suicide suspected
- Unexpected death
- Unexpected sudden death of adult
- Unexplained sudden death
Instructional NotesGuidance
Instructions from the official ICD-10-CM Tabular List that apply to R99: its own notes plus those printed at Chapter 18. A note printed at a category, block or chapter applies to every code under it.
Applicable To
Conditions this code is used for: synonyms of the title or, for "other specified" codes, the conditions assigned to it. The list is not exhaustive.
- Death (unexplained) NOS
- Unspecified cause of mortality
Excludes2
Not included here: the excluded condition is not part of this code, but a patient may have both, so both codes may be reported.
Notes
General instructions on how these codes are used.
- This chapter includes symptoms, signs, abnormal results of clinical or other investigative procedures, and ill-defined conditions regarding which no diagnosis classifiable elsewhere is recorded.
- Signs and symptoms that point rather definitely to a given diagnosis have been assigned to a category in other chapters of the classification. In general, categories in this chapter include the less well-defined conditions and symptoms that, without the necessary study of the case to establish a final diagnosis, point perhaps equally to two or more diseases or to two or more systems of the body. Practically all categories in the chapter could be designated 'not otherwise specified', 'unknown etiology' or 'transient'. The Alphabetical Index should be consulted to determine which symptoms and signs are to be allocated here and which to other chapters. The residual subcategories, numbered .8, are generally provided for other relevant symptoms that cannot be allocated elsewhere in the classification.
- The conditions and signs or symptoms included in categories R00-R94 consist of:
- (a) cases for which no more specific diagnosis can be made even after all the facts bearing on the case have been investigated;
- (b) signs or symptoms existing at the time of initial encounter that proved to be transient and whose causes could not be determined;
- (c) provisional diagnosis in a patient who failed to return for further investigation or care;
- (d) cases referred elsewhere for investigation or treatment before the diagnosis was made;
- (e) cases in which a more precise diagnosis was not available for any other reason;
- (f) certain symptoms, for which supplementary information is provided, that represent important problems in medical care in their own right.
Source: CMS ICD-10-CM Tabular List. How to read instructional notes.
Index to Diseases and InjuriesGuidance
Alphabetical index entries that point to this code.
Cot death R99
Crib death R99
Syndrome See Also: Disease;
crib death R99
Clinical ClassificationClinical
AHRQ’s CCSR groups this code into broader clinical categories.
Clinical InformationClinical
Death
irreversible cessation of all bodily functions, manifested by absence of spontaneous breathing and total loss of cardiovascular and cerebral functions.Sudden Infant Death
the abrupt and unexplained death of an apparently healthy infant under one year of age, remaining unexplained after a thorough case investigation, including performance of a complete autopsy, examination of the death scene, and review of the clinical history. (pediatr pathol 1991 sep-oct;11(5):677-84)
Convert R99 to ICD-9-CMHistory
Code HistoryHistory
Questions About R99Overview
What is the ICD-10 code for ill-defined and unknown cause of mortality?
The ICD-10-CM code for ill-defined and unknown cause of mortality is R99. It is billable on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
Is R99 (Ill-defined and unknown cause of mortality) a billable code?
Yes. This is a billable ICD-10-CM code, specific enough to report ill-defined and unknown cause of mortality on HIPAA-covered claims from October 1, 2026 through September 30, 2027.
What MS-DRG does R99 group to?
When ill-defined and unknown cause of mortality is the principal diagnosis on an inpatient stay, it groups to MS-DRG 951 (other Factors Influencing Health Status), which carries a relative weight of 0.5574. Higher weights mean higher Medicare reimbursement.
Can R99 be a principal diagnosis?
Use it with care. This is a symptom code, so once a definitive diagnosis explaining the ill-defined and unknown cause of mortality is established, that condition takes the principal position instead.
What is the ICD-9 equivalent of R99?
Under the General Equivalence Mappings, ill-defined and unknown cause of mortality converts to ICD-9-CM 798.0 (sudden infant death synd) and 799.9 (unkn cause morb/mort NEC). The mapping is approximate, so confirm the match fits the documentation.
